1. Field of the Invention
The present invention relates to an image processing apparatus, an imaging apparatus, and an image processing method.
2. Description of the Related Art
In recent years, with development of digitalization of information, development of digitalization in a field of imaging apparatuses is also significant. Particularly, in imaging apparatuses represented by digital cameras, a solid image pickup device is used in place of conventional films for an imaging surface. As solid image pickup device (hereinafter, simply image pickup device), a charge coupled device (CCD) sensor or a complementary metal oxide semiconductor (CMOS) sensor, or the like is used.
As described, an imaging apparatus using an image pickup device captures and extracts light from a subject by an optical system by converting the light into electric signals by a solid image pickup device. Such an imaging apparatus includes a video camera, a barcode reader, a mobile phone, a mobile information terminal (PDA: personal digital assistant), an industrial camera, and the like, besides a digital camera.
As the imaging apparatus described above, there is an imaging apparatus that is used for a purpose supporting so called extended depth of field (EDoF) that extends depth of field by inserting a phase plate in the optical system. A depth of field is a distance range of allowable distance in an optical axis direction of a lens considered as focused on a subject at a certain distance from the lens of a camera. The phase plate inserted in the optical system has a function of giving a point spread function (PSF) to incident light of a subject to an image pickup device, and makes an image captured by the image pickup device blur but uniform in a deep depth of field. Therefore, the image made blur by the phase place is necessary to be corrected so as to be given a predetermined modulation transfer function (MTF). To restore such an image made blur by a phase plate, an inverse conversion processing of the point spread function is performed to improve MTF. Thus, the image is restored into a high resolution image.
Moreover, an image pickup device in a color camera as an imaging apparatus, sensitivity of detecting light corresponding to G (green) is highest among R (red), G (green), and B (blue), and if an image detected (captured) by the image pickup device is displayed as it is, the image tends to be a greenish image as a whole. Correction performed on such an image is white balance processing. The white balance processing is to correct variations in sensitivity for R, G, and B of an image pickup device, and is processing to adjust pixels by giving an appropriate gain to R, G, B pixels and give correction so that a white subject is displayed white.
As an imaging apparatus that performs restoration processing to restore an image that has been made blur by an optical system by performing such white balance processing, an imaging apparatus that performs restoration processing on a Y signal of a pixel after giving a white balance gain has been proposed (Japanese Patent Application Laid-open No. 2012-049759).
Furthermore, the image pickup device has a limit value maximum value) in a detectable light amount, and pixels to which an amount of light equal to or more than the light amount enters all take the same value (maximum value) and an accurate light amount cannot sometimes be detected. Particularly, as described above, because the device for detecting G (green) has high sensitivity among image pickup devices, an image that is imaged when light corresponding to G (green) enters in an amount equal to or more than the maximum detectable amount is to be unable to be restored properly by the inverse conversion processing. This is especially problematic when the image pickup device is a color camera, and such a problem occurs that a false color is produced when an accurate light amount is detected and restoration is also done properly for one color (for example, R (red) or B (blue)), while an accurate light amount is not detected and restoration is not done properly for another color (for example, G (green)).
However, the white balance processing in the imaging apparatus described in Japanese Patent Application Laid-open No. 2012-049759 gives a gain of 0 for colors except for a special color, and differs from general white balance processing to correct an entire image. Moreover, a method to solve the problem of producing a false color as one color (for example, G (green) is saturated and an accurate light amount is not detected and restoration is not done properly is not described therein.
In view of the above problem, there is a need to provide an image processing apparatus, an imaging apparatus, and an image processing method in which production of a false color is suppressed at the time of image processing.